Tappet face



April 1960 G. R. BOUWKAMP 2,933,949

TAPPET FACE Filed Sept. 9, 1957 3 Sheets-Sheet l E mvsmon.

April 1960 e. R. BOUWKAMP 2,933,949

TAPPET FACE Filed Sept. 9, 1957 3 Sheets-Sheet 2 "wa /M G. R'. BOUWKAMP 2,933,949

April 26, 1960 TAPPET FACE 3 SheetsSheet 3 Filed Sept. 9, 1957 IN VEN TOR.

617440 ,e awn 4 115 BY win/ 147 [vi/V4715 TAPPET FACE Gerald R. Bouwkamp, Royal Oak,

Standard Screw Company, ration ofNewJersey- Mich., assignor to Hartford, Conn., a corpo- This invention relates to hydraulic or mechanical tappets or valve litters and has for one purpose to provide a tappet having a curved cam-contacting surface with more than one radius of curvature. j. 7

Another purpose is to provide a cam face for a hydraulic or mechanical tappet effective to produce tappet rotation with reduced peak contact stresses.

Another purpose is to provide a hydraulic or mechanical tappet cam face effective to produce tappet rotation with reduced peak contact stresses and a minimum edge loading between said cam face ,and a cam with which it is operatively associated.

Another purpose is to provide for uniform, wear of a tappet cam face while maintaining a minimum reduced peak contact stress and preventing excessive edge loading between said cam face and a cam with which it is operatively associated.

Other purposes will appear from time to time during. the course of the specification and claims.

I illustrate my invention more or less diagrammatically in the accompanying drawings, wherein:

cited St ws P m 2,933,949 Patented Apr. 26,1960

as the radius of curvature in the direction of the path at the point of contact.

Like parts and symbols are indicated by like numerals and letters throughout the specification and drawings. Referring now to the drawings, and particularly to Figures 1 and 2, the numeral 1 generally represents a conventional cam shaft The numeral 2 similarly designates generally a conventional cam. A tappet or valve lifter is shown generally at 3. The valve lifter has a cam face 4 constituting its lower surface and positioned for operational contact with the cam 2..

Figure 1 is a side view illustrating aconventional cam and a hydraulic valve lifter or tappet;

Figure 2 is an endview in cross section taken on line 2-2 of Figure l;

Figure 3 is a schematiciietailview of a conventional spherical tappet cam face and a schematic representation of a tapered cam;

Figure 4 is a diagrammatic ilustration of conventional cam and tappet cam-face contact areas;

Figure 5 is a graphic'representation of a conventional tappet cam .face radius; 7

, Figure 6 is a schematic representation of one form of tappet cam face of my invention and'aschematic representation of tapered cam;

Figure 7 is a representation of tappet cam face and cam-contact areas of the device illustrated in Figure 6;

Figure 8 is a graphic representation of the tappet cam face radii illustrated in Figure 6;

Figure 9 is a schematic showing of a variant form of tappet cam face of my invention and a schematic representation of a tapered cam;

Figure 10 is a representation of the tappet cam face and cam-contact areas of the device illustrated in Figure 9; V

Figure 11 is a graphic representation of the tappet cam face radii illustrated in Figure 9;

Figure 12 is a diagram illustrating the geometric construction of a modified form and described in the specification;

Figure 13 is a diagram illustrating the geometric construction of the form of Figures 6, 7 and 8; and

Figure 14 is a diagram illustrating the geometric construction of Figures 9, l0 and 11.

The graphic representations of Figures 5, 8 and- 11 are drawn with the absissa as the path of the initial contact point across the tappet cam face and the ordinate degree to which the Figure 3 illustrates a typical spherical tappet cam face of conventional design and arranged to operate against a slightly tapered cam. The contact area at maximum lift and the two contact areas at maximum tappet velocities are illustrated by the shaded areas shown in the center and each side, respectively, of the diagram constituting Figure 4. I

Referring particularly to Figure 4, the outer circle 5 illustrates a tappet diameter. The dotted lines 6, 6 designate the width of the cam 2 of the path of the cam 2. The dot and dash line 7 indicates the path of the initial contact point as the contact area moves back and forth across the cam face of the tappet with rotation of the cam as may be seen best in Figure 4. The path 7, in the case of the conventional design illustrated schematically in Figures 3, 4 and 5, is a straight line at a constant distance from a plane to the center line of the tappet and perpendicular to be axis of the cam.

For a given set of conditions, an increase in the spherical radius of the tappet will resultin an increase in the length or major axis of the contact area and a 'reduction or lessening of the width or minor axis thereof. While such increase in the spherical radius of the tappet cam face results in a reduction of stress at the initial contact point at the center of the contact area where the peak stress occurs, such increase is limited by the requirement for precluding the contact area from run ning off the edge of the cam and consequent high loads" at the cam edge 'as well as higher peak stresses at the initial contact point. Similarly, the variation in amount ofolfset effects the amount of edge loading and the angle of the tapered cam can be controlled with respect to the center line of the tappet will effect the size of the tappet spherical radius. With larger spherical radii there is a greaterv eifect on the amount of offset for a given change of angularity of the tapered cam. As indicated in tional spherical radius is constant.

Figures 6, 7 and 8 illustrate one form of my invention in which the radius of curvature of the cam face is constant from the center of the tappet'out to a given diameter and from that diameter to the tappet CD. it is constant but smaller or shorter than the initial radius.

In Figure 8 it will be noted that the path of the initial point of contact is ofiset within the circle Sat which the two cam face surfaces are tangent. It will be ob served .further that the contact areas, illustrated for example-at 4a, since they do not atthese positionsfcross the circle at which thetwo surfaces are tangent, are

' elliptical in shape and their size and peak stresses will depend on the radius of curvature of the surface on which they occur. When the contact area lies across the tangent circle, the curve of compression will no longer be symmetrical, as indicated at the contact area at maximumlift anddesignated 5a in Figure 7. The major axis of the portion ofcontact area 5a falling outside the. tangent circle 8 will tend to beshortened-or blunted and.

and therefore the width Figure 5, the conven A A 4 J aesacea of the major axis falling inside the tangent circle.

By selecting the proper diameter for the tangent circle, the contact area movement can be made less sensitive to variations in the angle of the tapered cam with respect to the tappet center line. Since the peak contact stress generally occurs near the nose of the cam when the contact area is near the center of the tappet, a reduction can be obtained through the use of two radii of curvature for the tappet cam face. The large center radius of the curvature combined with the smaller outer radius of the curvature, with the resultant non-symmetricalcontact area, will permit lower peak stresses in the tappet than is possible with the conventional spherical, constant radius cam face while maintaining the same degree of protection against edge loading. Alternatively, increased protection against edge loading with the same peakstress is possible with the tappet cam face having two radii of curvature. The smaller radius of curvature of the outer curve will increase the stress level on the contact area when it falls outside the tangent circle. However, since these stresses are much lower than those near the nose of the cam, the use of two radii of curvature will have the effect of more uniformlydistributing the stress level and wear over the cam face of the tappet.

The offset of the contact area will also be reduced when it lies on the outer surface having the smaller radius of curvature. With reduced offset the contactarea will not come as close to the tappet CD. at a given peak tappet velocity. Moreover, more positive control of tappet rotation is provided through control of .the offset of contact area with the tappet cam face having two spherical radii.

As illustrated graphically in Figure 9, the two spherical radii of the tappet cam face of my invention may be rather sharply defined.

In Figures 9, 10 and 11 I illustrate a tappet cam face having. a radius of curvature varying according to a smooth curve, illustrated graphically, for example, in Figure 11, when proceeding from the center of the cam face to the outside edge. As best seen in Figure 10,2

the, path of the initial point of contact, indicated at 7b,. isrepresented by a smooth arched line. The contact:

area at maximum lift, indicated at b, has an even more blunted end portion.

In the geometric construction of Figure 12 R is the radius ofcurvature of the .carnface within the diameter Dx. R is the radius of curvature of the camface between the'diameters Dx and Dy. R is. the radius of curvature of the ca mface outside the diameter Dy. Dx.

and Dy. are the diameters at which the three surfaces are tangent.

In the geometric construction of Figure 13 R is the radius of curvature of the camface within the diameter R is the radius of curvature of the camface ou ts1de the diameter Dx. Dx is the diameter at which the two surfaces are tangent.

tor a given load this will s'lig'htly mere-5s thelen'g'th 4 "in the geometric construction of Figure 14 the curved line from C to C isthe locus of the centers of the radii of curvature. Rx is the radius of curvature at a diameter Dx. Dx is the diameter at which the two surfaces are tangent. 1

Although an operative form of the device has been shown, the invention is not limited to the particular details shown. Many changes may be made in the form, shape and arrangement of parts without departing from the spirit of the invention. It will be understood, for example, that a tappet cam face made up of three or more curved surfaces, each with its own constant radius of curvature and tangent to the adjoining surfaces, may be employed where desirable without departing from the nature and scope ofthe invention.

I claim:

1. A tappet having a cam face, said cam face having a plurality of radii generating spherical surfaces.

2. A tappet having a cam face, said cam face having a plurality of radii generating spherical surfaces, each of said radii defining a circle concentric with a circle defined by an adjoining radius.

'3. A'tappet having a cam'face, said cam face having acurved' surface; said curved surface a plurality of porfions, each of said portions having'a different radius of curvature.

4. The structure of claim 3 wherein each said radius of curvature defines a circle tangent to a circle definable by an adjacent radius of curvature.

5'. The structure of claim 3 wherein said portions are two in number, the radii of curvature of said portions being positioned to define a tangent circle.

6. A'tappe't having a cam face, said cam face having a curved surface, said surface having a portion defined by a first radius and a secone portion defined by a second radius, the curved surfaces formedby the two radii being" tangent at the circle concentric with the center 7 line of the tappet;

7. A tappet having a camfac e', said camface having a plurality of radii generating spherical surfaces, each of References Cited in the file of this patent g V UNITED STATES PATENTSI 2,642,051 Ru sel" -a .June 16, 1953 2,694,389 Turkish --Nov. 16, 1954 FOREIGN PATENTS 239,579 Great Britain Sept. 7, 1925 France Aug; 3, 1951 

